(1) Field of the Invention
The present invention relates generally to safety switches, and more particularly to a passive switch assembly mounted on an unmanned, tube launched vehicle which, by interaction with the bore of the vehicle launch tube, identifies whether the vehicle is in or out of the launch tube.
(2) Description of the Prior Art
In most applications when an unmanned vehicle is launched from a tube, the safety logic of the vehicle does not allow the vehicle to begin operation until the vehicle is clear of the launch tube. In the case of an underwater vehicle being launched by an impulse of high pressure water from a ram, the typical safety logic senses the correct acceleration from the impulse and detects the presence of seawater when an umbilical cable or lanyard breaks away from the vehicle. However, during some phases of testing, it may be desirable to have the vehicle swim out of the tube under much lower pressure. The current safety logic would prevent the operation of the vehicle under these conditions. In addition, it may be necessary to have the umbilical remain attached to the vehicle in order to provide power to the vehicle or to obtain run-time measurements until the umbilical breaks. Again under these conditions, the safety logic would prevent the operation of the vehicle. Further, the reliance of the safety logic on the separation of an umbilical cord or lanyard may present unnecessary hazards to the operation of the vehicle. The umbilical cord or lanyard may become entangled in the propulsion unit of the vehicle which may lead to a false tube exit signal. Also, routing of a lanyard within the confines of a launch tube may be difficult and may require special considerations with respect to the launch method used.
A number of prior art safety devices for tube launched underwater vehicles are actuated as a result of the vehicle entering the water with sufficient forward velocity, e.g., U.S. Pat. No. 2,428,565 to Guidosh, U.S. Pat. No. 2,589,547 to Hughes et al. and U.S. Pat. No. 2,787,957 to Dippel. As with prior art devices relying on sensing proper acceleration, devices relying on the flow of water will not operate properly for a vehicle allowed to swim out of the launch tube nor will they operate when a vehicle is launched in the air.
Cooke et al., U.S. Pat. No. 3,004,506, provide a safety switch which does not depend on water flow for activation. The switch has two levers which are interconnected at a bearing. The first lever is pinned to a switch plunger and the second lever is pinned to the vehicle housing. The switch plunger is spring biased to pull down and rotate the first lever. When the vehicle is in the launch tube, the second lever is in contact with the inside of the tube which prevents it from rotating and, due to the interconnecting bearing, also prevents the first lever from rotating under the influence of the spring biased plunger. When the vehicle exits the launch tube, the second lever is free to rotate which allows the second lever to rotate, leading to the switch plunger moving away from the switch contacts thus activating the switch. While the Cooke et al. switch overcomes some of the disadvantages of other prior art switches, the two levers, the bearing connection and the cam-like action of the second lever and switch plunger connection present a complex design with an increased probability of failure. Fouling or corrosion between the levers, at the bearing connection, or at the lever-plunger connection can prevent the proper operation of the Cooke et al. switch.